The angiotensin-coverting enzyme [ACE, dipeptidylcarboxypeptidase (EC 3.4.15.1)] is a member of rennin-angiotensin system regulating blood pressure. It is known that ACE leads some physiological changes (blood pressure elevation, for example) by converting angiotensin I to active angiotensin II and inactivating bradyskinin (Non-patent Document 1). So, there are so many inventions about medicine (blood pressure-lowering drug, for example) of which action mechanism is down regulation of blood pressure by inhibiting ACE (Patent Documents 1-4).
The cell membrane is consisted with proteins and lipids, where many biological processes, such as energy production, signal transduction, cell-to-cell interaction and secretion, take place. The GPI-anchored protein is a main component of cell membrane, which bounds there via GPI-anchor, crucial for many biological processes. However, the normal prion protein also binds the GPI-anchor and when the pathogenic form of prion binds to the normal counterpart, prion-related diseases such as Creutzfeldt-Jakob disease, Gerstmann-Straussele syndrome and kuru disease, may occur. A bacterial toxin, lipopolysaccharide (LPS) binds to its receptor CD14, which is also a GPI-anchored protein, and exhibits cytotoxicity.
In addition, when the sperm binds to zona pellucida of egg, GPI-anchored proteins (ex. PH-20 and TESP5 in mouse; Non-patent Documents 2, 3) should be released from the sperm surface and, if not, male infertility might occur.
The release of GPI-anchored protein from the cell surface is effective for relieving or curing prion-related diseases, bacterial infection and some kind of male infertility. As a protein showing GPI-anchor-cleaving activity (GPIase activity), GPI-PLD is only enzyme known so far in mammals. However, GPI-PLD has been reported to exhibits the GPIase activity only when it is expressed intracellularly in culture cells (Non-patent Document 4). Therefore, GPI-PLD might not be useful as medicine in the light of use of GPIase activity for medication.
It has been reported that ACE cleaves numbers of substrates other than angiotensin I and bradykinin, such as enkephalin and pre-enkephalin such as heptapeptide and octapeptide. Further, ACE is known to hydrolyze tridecapeptide and neurotensin, as well as to inactivate substance P by digesting. However, the GPI-anchored protein releasing activity of ACE has never been reported.
Patent Document 1: JP10-036391 A
Patent Document 2: JP2001-064299 A
Patent Document 3: JP2001-233789 A
Patent Document 4: JP2002-138100 A
Non-patent Document 1: Hooper et al., Int. J. Biochem. 23:641-647, 1991
Non-patent Document 2: Honda et al., J. Biol. Chem. 277:16976-16984, 2002
Non-patent Document 3: Lin et al., J. Cell Biol. 125:1157-1163, 1994
Non-patent Document 4: Tujioka et al., Biochem. Biophys. Res. Commun. 251:737-747, 1998
Non-patent Document 5: Skidgel et al., Neuropeptides and Their Prptidases, Turner A J Ed., Chichester, UK, 1989